1. Field of the Invention
This invention relates to a process for the production of titanium and zirconium by the use of arc heater furnaces.
2. Description of the Prior Art
Many metals can be reduced or displaced from their compounds by more active metals. This technique is fairly common in the preparation of many of the rarer metals. Metals which melt at low temperatures, such as aluminum and magnesium, can be easily handled. However, metals having very high melting points such as titanium and zirconium are more difficult. One reason for the difficulty is that the higher melting metals are very reactive in their molten state and conventional ceramic crucibles are quickly deoxidized and destroyed thus contaminating the metal product. Graphite crucibles contain them but also contaminate the metal product.
The reduction process most commonly used to produce titanium and zirconium is the Kroll process. In this process the ores are heated with carbon in an electric furnace in the presence of chlorine gas causing the formation of metal chlorides, carbon monoxide and carbon dioxide gas. The chlorides are then distilled and condensed to effect purification. In the production of titanium a steel-walled furnace is used and is preliminarily heated to about 750.degree. C. It contains helium gas and clean magnesium bars. Liquid titanium tetrachloride (TiCl.sub.4) is caused to drip on the magnesium bars where it reacts isothermally to form titanium metal. The metal forms as a strong sponge containing magnesium chloride and magnesium metal. These products are then removed from the reaction chamber by a machining operation, and the chips are purified by leaching with dilute hydrochloric acid or by vacuum distillation. Finally, the sponge chips are compressed into consumable electrodes, which are then vacuum arc melted to produce solid ingots. If there is a high level of impurities in the original sponge, it may have to be remelted more than once. The zirconium process is similar to the titanium process, except that the zirconium tetrachloride (ZrCl.sub.4) is solid when it enters the reaction chamber. Although magnesium is the preferred metal for producing titanium and zirconium, other active metals such as sodium may be used as reducing agents. Generally, the Kroll process with its many sequential steps has the disadvantage of being extensive which is the main reason for the high price of titanium and zirconium.